Electron multiplier



Jan. s, 1952 2,581,460

A. I. VANGEEN ELECTRON MULTIPLIER Filed Aug. 7, 1947 INVENTOR ABRAHAM l, VA/ VEEN SYM/4%@ ATTO RN EY Patented Jan. 8, 1952 ELECTRON MULTIPLIER Abraham Isidore Vangeen, London, England, assignor to International Standard Electric Corporation, New York, N. Y.

Application August 7, 1947, Serial No. 767,018 In Great Britain February 3, 1939 Sefction 1, Public Law 690, August 8, 1946 Patent expires February 3, 1959 9 Claims.

This invention relates to electron discharge devices of the electron multiplier type. It is primarily concerned with such devices having a thermionic primary electron source, but is generally applicable where secondary emissive electrodes tend to lose their emissive power.

It is already known that an electron multiplier employing a hot oxide-coated cathode as the source of primary electrons tends to have a short life. Various explanations of this short life have been put forward, but the most generally accepted one is that the atoms, for example barium atoms in the case of a, barium xide coating, are evaporated from the oxide-coated cathode and are deposited on the secondary-emissive surface or surfaces. Thus, with the passage of time, a contaminating layer is gradually built up on the sensitive surface and the net secondary emission ratio falls to a value characteristic of the con# taminating material.

Proposals have been made ro shield the secondary-emissive surface or surfaces from the evaporating atoms; `other proposals have been made to operate the secondary emitter at a sufficiently high temperature to re-evaporate atoms settling upon it.

It is now proposed to provide for the deposition of active material upon the secondary-emissive surface or surfaces during operation of the device. The deposition may be effected continuously under normal operating conditions, for example, from an adjacent carrier of the active material which becomes heated under such operating conditions, or the deposition can be effected at desired intervals, for example by applying abnormal voltages or currents to some r all of theelectrodes. The carrier may incorporate a heater so that its temperature can be more readily controlled. The carrier may be constituted by a grid like anode disposed in iront of the secondary electron emissive surface, the temperature of the anode being determined solely by electron bombardment and conduction from neighbouring electrodes or primarily by an individual heater or heating current. Alternatively the carrier may be constituted by a small container for the active material, heating means being provided for the container.

According to one method of Vputting the invention into effect, there is shown as active material a substance with an appreciable vapour pressure at a temperature of. say 300 C. During the manufacture of the electron multiplier this substance is deposited by spraying, dipping or some other suitable coating method upon a grid-shaped anode immediately in front of the secondary emission electrode.. During processing this gridshaped anode is raised to a high temperature so that some of the active material evaporates off and deposits on the secondary emission electrode to form the initial layer. This tube is then sealed off from the exhaust pump, and may or may not be submitted to an activation process.

The operating conditions are such that active material is continuously evaporated off from the anode on to the secondary cathode. Th-us, throughout the life of the tube the sensitive surface is always being renewed and the arrival of contaminating atoms from the primary cathode becomes of minor importance.

Almost any secondary emission material with a high enough vapour pressure may be used in this manner, but particular success has been obtained with alkali and alkaline earth borates.

The accompanying drawing, Figs. 1 and 2, illustrate structures incorporating the invention wherein the active material is stored in a small container adjacent to the secondary emissive surfaces but out of the electron path.

Each figure 'shows a section through the axis of the electrode structure which will be mounted in an evacuated envelope. In each case C is a tubular indirectly heated cathode, Gl a control grid, G2 an accelerating grid, A a collecting electrode or anode of grid formation and SE secondary-electron emissive plates. Small'containers or capsules K are loaded with active material S for deposition on the emissive plates SE and carry a heater resistance R having suitable leading-in connections.

The initial emissive layer upon the plates SE may be deposited after the assembly and evacuation of the device, this deposition being effected by passing a suitable current through the heater or heaters R. During subsequent operation of the device, the emissive plates may be continuously or intermittently activated by suitably energising the heater to vapourise the stored material.

While I have described above the principles of my invention in connection with specic apparatus, it is to be clearly understood that this dea high temperature during normal operation of the device, said electrode being coated with said borate.

4. Electron discharge device according to claim l 1 wherein said vaporizing means includes a capsule containing said borate positioned adjacent the secondary emissive surface of said electrode and a heating element for controlling the temperature of the capsule.

5. Electron discharge device comprising a secondary electron-emissive electrode wherein the secondary emissive material of saidelectrode comprises a borate of a metal selected from the group including alkali and alkaline earth metals.

6. Electron discharge device comprising an en-` velope, a secondary electron-emissive electrode within said envelope, a quantity of an alkali borate within said envelope spaced from said electrode and vaporizing means spaced from said electrode for depositing said alkali borateupon Y said electrode during operation of said device.

'7. Electron discharge device comprising an envelope, a secondary electron-emissive electrode within said envelope, a quantity of an alkaline earth borate within said envelope spaced from said electrode, and vaporizing means spaced from said electrode for depositing said alkaline earth borate upon said electrode during operation of said device.

8. Electron discharge device comprising an envelope having therein a source 'of primary electrons, a secondary electron-emissive electrode located in the path of said primary electrons from said source and having a secondary emissive surface incident to said path, a given Yquantity of borate of a metal selected from the group including alkali and alkaline earth metals disposed outside of said path, and directive vaporizing means disposed outside the path of said incident electrons and including a vaporizing portion directed obliquely to said secondary emissive surface of said electrode for depositing said borate upon said surface during operation of the device.

9. Electron discharge device comprising an envelope having therein a source of primary electrons, a secondary electron-emissive electrode located in the path of said primary electrons from said source and having a secondary emissive surface incident to said path, a given quantity of an active secondary emissive material within said envelope and adjacentsaid secondary electronemissive electrode, and directive vaporizing means disposed outside the path of said incident electrons and including a vaporizing portion directed obliquely to said secondary emissive surface of said electrode for depositing said active secondary emissive material upon said surface during operation of the device.

ABRAHAM ISIDORE VANGEEN.

REFERENCES oi'rED The following references are of record in the le of thispatent:

UNITED STATES PATENTS Number Name Date 2,027,025 De Boer et al. Jan. 7, 1936 2,159,774 Veenemans et al. May 23, 1939 2,228,945 Bruining et al Jan. 14, 1941 

5. ELECTRON DISCHARGE DEVICE COMPRISING A SECONDARY ELECTRON-EMISSIVE ELECTRODE WHEREIN THE SECONDARY EMISSIVE MATERIAL OF SAID ELECTRODE COMPRISES A BORATE OF A METAL SELECTED FROM THE GROUP INCLUDING ALKALI AND ALKALINE EARTH METALS, 